The present invention relates to the use as filler, in polymer compositions, of calcined hydrotalcite and/or hydrotalcite intercalated using at least one anionic surface-active agent.
It also relates to the polymer compositions thus obtained.
Finally, it also relates to finished articles based on these compositions, in particular tire covers.
It is known to employ reinforcing white fillers in polymers, in particular elastomers, such as, for example, precipitated silica. However, the results are not always those hoped for.
The aim of the invention is to provide another filler for polymer compositions which provides them with a highly satisfactory compromise with regard to properties, namely, preferably:
good rheological properties and excellent suitability for vulcanization, at least comparable with those of highly dispersible precipitated silicas,
particularly advantageous dynamic properties, in particular a Payne effect of relatively low amplitude, resulting in a rather low resistance to rolling for tires based on these compositions, and/or a rather high tangent xcex4 at 0xc2x0 C., resulting in an improved adhesion for tires based on these compositions,
good strengthening in terms of modulus,
a generally high resistance to thermal aging and to UV (ultraviolet radiation) aging.
With this aim, a subject matter of the present invention is the use as filler, in particular as reinforcing filler, in a composition comprising polymer(s), of at least one calcined hydrotalcite and/or hydrotalcite intercalated by at least one anionic surface-active agent.
The hydrotalcite used in the context of the invention is thus at least one of the following compounds:
(a) a calcined hydrotalcite,
(b) a hydrotalcite which is calcined and then intercalated using at least one anionic surface-active agent (intercalated calcined hydrotalcite),
(c) a hydrotalcite intercalated using at least one anionic surface-active agent (intercalated hydrotalcite).
Use is advantageously made, in the context of the invention, rather of a calcined hydrotalcite (a), optionally additionally intercalated (b).
Even if the hydrotalcite used as filler according to the invention can comprise at least one monovalent cation, such as, for example, Li, and at least one trivalent cation, it usually contains rather at least one divalent cation and at least one trivalent cation; the divalent cation to trivalent cation molar ratio is then generally between 1 and 8, and preferably between 2 and 6.
The divalent cation can be in particular Mg, Ni, Zn or Co.
The trivalent cation can be, for example, Al, Ga, Fe or Cr.
Advantageously, the divalent cation is Mg and the trivalent cation is Al (magnesium aluminum hydrotalcite); the Mg/Al molar ratio is then generally between 1.5 and 5, preferably between 2 and 4, particularly between 2 and 3.
The starting hydrotalcite (that is to say, noncalcined and nonintercalated) can be prepared by any process known to a person skilled in the art. Thus, it can, for example, be obtained by neutralizing, by addition of a sodium carbonate solution, a vessel heel comprising the two types of cations mentioned above, in this instance at least one divalent cation (or monovalent cation) and at least one trivalent cation; the temperature of the reaction medium can be maintained between 50 and 95xc2x0 C., in particular between 60 and 90xc2x0 C., the pH being, for example, between 10 and 12.
The starting hydrotalcite can be obtained by simultaneously adding, to a vessel heel formed of water, a solution comprising acid salts of the two cations (or two solutions each comprising an acid salt of one of the two cations), a sodium carbonate solution and a sodium hydroxide solution (the latter serving in particular to adjust the pH, in particular to a value of between 10 and 12, for example to 11); the duration of the simultaneous addition can vary between 30 and 90 minutes, for example between 45 and 60 minutes; the temperature of the reaction medium can be maintained between 25 and 95xc2x0 C.; in particular, the temperature during the simultaneous addition can be maintained between 25 and 35xc2x0 C., for example at 30xc2x0 C. approximately; on conclusion of this simultaneous addition, the temperature can be brought and maintained between 85 and 95xc2x0 C., for example at approximately 90xc2x0 C., in particular for 1 to 3 hours, for example for 2 hours.
The starting hydrotalcite can be a basic magnesium aluminum carbonate, for example of formula MgCO3.5Mg(OH)2.2Al(OH)3.yH2O (in which yxe2x89xa70, for example y=4).
The hydrotalcite used in the context of the invention, in particular the calcined hydrotalcite (a), optionally intercalated (b), preferably has a BET specific surface of between 100 and 300 m2/g, generally between 120 and 220 m2/g, in particular between 130 and 200 m2/g; it is, for example, between 150 and 180 m2/g. The BET surface is determined according to the method of Brunauer-Emmet-Teller described in The Journal of the American Society, Vol. 60, page 309, February 1938 and corresponding to Standard NF T 45007 (November 1987)
It generally has a CTAB specific surface of between 100 and 300 m2/g, in particular between 120 and 210 m2/g, especially between 130 and 190 m2/g; it can be between 150 and 180 m2/g. The CTAB surface is the external surface determined according to Standard NF T 45007 (November 1987-5.12).
The calcined hydrotalcite employed preferably results from a calcination treatment of a hydrotalcite (referred to as xe2x80x9cstarting hydrotalcitexe2x80x9d) at a temperature of at least 250xc2x0 C., in particular of at least 300xc2x0 C.; the calcination temperature is preferably between 300 and 600xc2x0 C. and more preferably still between 300 and 550xc2x0 C.; it is, for example, between 300 and 500xc2x0 C., in particular between 350 and 500xc2x0 C.
Said calcined hydrotalcite is advantageously decarbonated. In fact, the decarbonation is generally obtained by the calcination treatment itself.
The calcined hydrotalcite used generally exhibits a carbonate anion/trivalent cation molar ratio of less than 0.3 (decarbonated hydrotalcite), preferably of less than 0.25; this ratio can, for example, be at most 0.15.
It should be noted that at least one anionic surfactant can be intercalated in the structure of the calcined hydrotalcite before it is used (intercalated calcined hydrotalcite).
For this to be done, the calcined hydrotalcite can thus be mixed with a solution of at least one anionic surface-active agent, in particular at a temperature of between 50 and 90xc2x0 C., for, for example, 1 to 4 hours; the suspension obtained can then be centrifuged and the centrifugation cake dried, in particular in an oven, at a temperature which can vary in particular between 40 and 60xc2x0 C. Advantageously, recourse to rigorous conditions, in particular to flushing with nitrogen, during the intercalation procedure is not necessary.
The calcined hydrotalcite can be stored for a long time in a dry atmosphere without recarbonating, which facilitates the intercalating stage.
Even though this does not constitute a preferred alternative form, a hydrotalcite intercalated by at least one anionic surface-active agent can also be used in the context of the invention.
Such an intercalated hydrotalcite can be obtained in particular by simultaneously adding, to a vessel heel formed of water, a solution comprising acid salts of the two cations (or two solutions each comprising an acid salt of one of the two cations), a solution of anionic surface-active agent and a sodium hydroxide solution (the latter serving in particular to adjust the pH, in particular to a value of between 10 and 12, for example to 11); the duration of the simultaneous addition can vary between 30 and 90 minutes, for example between 45 and 60 minutes; the temperature of the reaction medium can be maintained between 25 and 95xc2x0 C.; in particular, the temperature during the simultaneous addition can be maintained between 25 and 35xc2x0 C., for example at 30xc2x0 C. approximately; on conclusion of this simultaneous addition, the temperature can be brought and maintained between 85 and 95xc2x0 C., for example at approximately 90xc2x0 C., in particular for 1 to 3 hours, for example for 2 hours.
The surface-active agent which is used to form an intercalated hydrotalcite or, preferably, which can be introduced between the inorganic sheets of the calcined hydrotalcite (to form an intercalated calcined hydrotalcite) has an anionic polar part (head), generally complexing with respect to the trivalent cation (for example Al) of the hydrotalcite.
The anionic polar part of said surface-active agent is usually an alkali metal or alkaline earth metal phosphate, phosphonate, carboxylate, sulfonate, sulfate or succinate.
This anionic surface-active agent can be chosen, for example, from:
alkyl ester sulfonates of formula Rxe2x80x94CH(SO3M)xe2x80x94COORxe2x80x2, where R represents a C8-C20, in particular C10-C16, alkyl radical, Rxe2x80x2 a C1-C6, in particular C1-C3, alkyl radical and M an alkali metal cation (in particular sodium, potassium or lithium), a substituted or unsubstituted ammonium (methyl-, dimethyl-, trimethyl- or tetramethylammonium, dimethylpiperidinium, and the like) cation or a cation derived from an alkanolamine (monoethanolamine, diethanolamine, triethanolamine, and the like), said alkyl ester sulfonates preferably being methyl ester sulfonates in which the R radicals are C14-C16 radicals;
alkyl sulfates of formula ROSO3M, where R represents a C5-C24, in particular C10-C18, alkyl or hydroxyalkyl radical, M representing a hydrogen atom or a cation as defined above, and their ethoxylenated (EO) and/or propoxylenated (PO) derivatives having on average between 0.5 and 30, in particular between 0.5 and 10, EO and/or PO units;
sulfated alkylamides of formula RCONHRxe2x80x2OSO3M where R represents a C2-C22, in particular C6-C20, alkyl radical, Rxe2x80x2 a C2-C3 alkyl radical and M a hydrogen atom or a cation as defined above, and their ethoxylenated (EO) and/or propoxylenated (PO) derivatives having on average between 0.5 and 60 EO and/or PO units;
salts of saturated or unsaturated C8-C24, in particular C14-C20, fatty acids, C9-C20 alkylbenzenesulfonates, primary or secondary C8-C22 alkylsulfonates, alkylglycerol sulfonates, sulfonated polycarboxylic acids, paraffin sulfonates, N-acyl-N-alkyltaurates, alkyl phosphates, isethionates, alkylsuccinamates, alkylsulfosuccinates, the monoesters or diesters of sulfosuccinates, N-acylsarcosinates, alkylglycoside sulfates or polyethoxycarboxylates, the cation being an alkali metal (in particular sodium, potassium or lithium), a substituted or unsubstituted ammonium (methy-, dimethyl-, trimethyl- or tetramethylammonium or dimethylpiperidinium) residue or a residue derived from an alkanolamine (monoethanolamine, diethanolamine, triethanolamine, and the like).
Mention may in particular be made of alkali metal oleates, for example potassium oleate.
The fundamental components of the hydrotalcite employed according to the invention are usually present in the form of platelets, generally substantially hexagonal platelets; their largest dimension can be between 50 and 300 nm, preferably between 100 and 200 nm.
The compositions comprising polymer(s) in which the calcined and/or intercalated hydrotalcite, advantageously the calcined hydrotalcite (a) and, optionally, in addition intercalated (b), is used as filler, in particular as reinforcing filler, and which constitute another subject matter of the invention, are generally based on one or more polymers or copolymers, in particular on one or more elastomers, in particular thermoplastic elastomers, preferably exhibiting at least one glass transition temperature of between xe2x88x92150 and +300xc2x0 C., for example between xe2x88x92150 and +20xc2x0 C.
Mention may be made, as possible polymers, of diene polymers, in particular diene elastomers.
For example, mention may be made of natural rubber, polymers or copolymers deriving from aliphatic or aromatic monomers comprising at least one unsaturation (such as, in particular, ethylene, propylene, butadiene, isoprene or styrene), poly(butyl acrylate), or their blends; mention may also be made of silicone elastomers, functionalized elastomers (for example, functionalized by functional groups capable of reacting with the surface of the hydrotalcite) and halogenated polymers. Polyamides may be mentioned.
The polymer (copolymer) can be a bulk polymer (copolymer), a polymer (copolymer) latex or a solution of polymer (copolymer) in water or in any other appropriate liquid dispersant.
Said compositions comprising polymer(s) can be vulcanized with sulfur (vulcanizates are then obtained) or can be crosslinked, in particular with peroxides.
Another compound, such as precipitated silica, in particular a highly dispersible compound, can optionally also be employed as filler; while the amount by weight of precipitated silica employed can then be a minor amount with respect to that of the hydrotalcite, it can also be equal to or predominant with respect to that employed for the hydrotalcite; the hydrotalcite and the silica can then be introduced into the polymer(s) in the form of a mixture or separately. However, the compositions comprising polymer(s) often do not comprise precipitated silica as filler and/or the filler is formed entirely of calcined and/or intercalated hydrotalcite.
Generally, the compositions comprising polymer(s) additionally comprise at least one coupling agent and/or at least one coating agent; they can also comprise, inter alia, an antioxidant.
The invention, in particular in the case of the use of calcined hydrotalcite, can make it possible in particular to reduce the amount of coupling agent to be employed in compositions comprising polymer(s) while not being damaging to their properties in the vulcanized state.
The proportion by weight of hydrotalcite in the composition comprising polymer(s) can vary within a fairly wide range. It usually represents 4 to 80%, in particular 20 to 80%, for example 30 to 70%, of the amount of the polymer(s). It preferably represents 20 to 80%, for example 30 to 70%, of the amount of the polymer(s) when the compositions comprising polymer(s) do not comprise precipitated silica as filler and/or when the filler is formed entirely of calcined and/or intercalated hydrotalcite.
The present invention also relates to finished articles based on the compositions comprising polymer(s) described above (in particular based on the vulcanizates mentioned above).
Mention may thus be made of tire covers, in particular the sidewalls and the tire tread strip. Calcined hydrotalcite can be used in the tire internal rubber: it can in particular improve the impermeability (in particular to air) thereof, which can make it possible to avoid the use of a halobutyl elastomer (chlorobutyl or bromobutyl elastomer, for example) and/or to employ, preferably predominantly, natural rubber instead.
Mention may also be made, as finished articles, of floor coverings, shoe soles, components of vehicle caterpillar tracks, rollers for cableways, seals for domestic electrical appliances, seals for liquid or gas pipes, braking system seals, sheathings, cables, transmission belts, gas barriers or flame-retardant materials.
The following examples illustrate the invention without, however, limiting the scope thereof.